89 deville stays revved after acceleration

Sometimes after accelerating, my 89 Deville (123,000 miles) stays revved up even though the foot is off the accelerator.
When I notice the car keeps on speeding, I tap the accelerator and it goes back to normal.
No code is issued and no one really know what is causing this.
Has anyone heard of this?
It could be the computer.

Had a similar problem on my 93 had the Throttle Body cleaned and it has been fine since. KC